The present invention relates to a tool holder. The holder is included in a processing machine and constitutes a holder for a machining tool such as a lathe shaft. The holder is secured in the machine by a tool attachment which may either be permanent or be located on a unit containing several tool holders in order to enable several machining operations to be carried out one after the other. Frequently the machining tool must be rather long so that machining can be performed in the hollow interior of a workpiece. With long machining tools there is a considerable risk of the tool being subjected to vibration, thus resulting in a poorer quality of machining. Several attempts have been made to reduce the occurrence of vibration. The tool shaft has, for instance, been arranged in a cradle with several screw joints pressing the shaft against the cradle. The vibration was not reduced as desired and wear occurred at the mouth of the holder, giving rise to further vibration. The problem of vibration is troublesome as is evident, for instance, from Sandvik Coromant's publication entitled "Turning with dampened lathe shafts" HV-5300:008-SWE.
One method of reducing the undesired vibrations in the case of long machining tools is to replace mechanical attachment means by a hydraulic retention arrangement. This is achieved by providing a tool holder with an aperture to receive the shaft of the machining tool. Inside the wall of the aperture is a tubular space which can be filled with a medium such as oil or fat. If this medium is subject to pressure the walls of the aperture will be forced inwards, thereby clamping the shaft of the machining tool extremely firmly. The force achieved in this way exceeds any force which can be achieved by mechanical means. Inner sleeves or bushings having the same outer diameter as the inner diameter of the aperture, but with different inner diameters can be inserted into the aperture, thereby enabling the tool holder to be used for machining tools of different thicknesses.
Reference is made to applicant's copending application Ser. No. 07/828,994 filed Feb. 4, 1992 for additional background information on hydraulic tool holders.
The use of hydraulic tool holders has created certain problems in connection with the application of cooling liquid to the metal cutting surfaces. The additional space occupied by the hydraulic mechanism in front of the fixed tool holder tends to obstruct the conventionally mounted nozzles which have been employed to supply cooling fluid. In addition, the longer cutting tools made practical by the hydraulic chuck require nozzles which must project the cooling liquid greater distances and with increased precision than heretofore.